Field of the Invention
The present invention relates to a zoom lens suitable for a television, camera, a video camera, a film camera, a broadcasting television camera, and a movie camera, and more particularly, to a telephoto zoom lens having a large aperture and a high magnification.
Description of the Related Art
In a case where a nature program or the like is photographed for television program (for example, an animal, a bird, or the like is photographed outdoors from a long distance), a zoom lens that is usable up to a focal length in a super telephoto range at a high zoom ratio (for example, a high magnification of 7× or more and a half angle of field of 3 degrees or less at a telephoto end) and has high optical performance is required. In such photographing, a camera is often carried on a shoulder for photographing, and hence a zoom lens that is smaller in size and lighter in weight and has good portability is required. Moreover, in recent years, in addition to related-art video cameras and broadcasting television cameras, opportunities of photographing moving images are increasing as in a case where a camera for still photography, such as a single lens reflex camera, is also used for photographing a moving image. With a zoom lens for photographing a moving image, a zoom operation or a focus operation is performed during photographing, and hence in a case where a total lens length is changed at the time of the operation, an operation sound becomes noise to affect the photography, which is undesirable. Therefore, a demand for a zoom lens in which a first lens unit is not moved for zooming and which is of an inner focus type is increasing as a zoom lens suitable for moving image photography. In general, a size of a sensor (image pickup element) of the single reflex camera is larger than 1 inch type, and is larger than a sensor having a size of 1 inch type or less, which is mainly used in a video camera or a broadcasting television camera. Therefore, there is an increasing demand for the zoom lens having the high magnification and being usable in the super telephoto range, which is compatible with such a large sensor as to exceed 1 inch type, good in portability and functionality, and suitable for moving image photography.
In U.S. Patent Application Publication No. 2007/0109665, there is proposed a telephoto zoom lens including four lens units, which has an angle of field at the telephoto end of about 0.7 degree and a zoom ratio of about 15×, and is suitable for a ⅔ inch broadcasting television camera.
In U.S. Patent Application Publication No. 2012/0250163, there is proposed a zoom lens including four units, which has an angle of field at the telephoto end of about 3.0 degrees and a zoom ratio of about 10×, and is compatible with a 1 inch type or larger sensor.
In a case where the zoom lens in U.S. Patent Application Publication No. 2007/0109665 adapts to a still larger image pickup element and is increased in zoom ratio while maintaining a large aperture ratio, an effective diameter on an image side of a zoom lens unit is increased, and hence the entire zoom lens is difficult to downsize.
In a case where the zoom lens in U.S. Patent Application Publication No. 2012/0250163 is further increased in telephoto range and zoom ratio while maintaining a total lens length, a diameter of an aperture stop is increased, and hence the entire lens is difficult to downsize.